IMS is a network architecture introduced by the 3GPP for mobile networks, and then employed by TISPAN for fixed networks. This architecture allows the dynamic establishment and the control of multimedia sessions between two clients as well as the reservation of resources at the media streams transport network level. It also manages the interaction of services.
A client user of an operator's telecommunications network is considered. In the 3GPP standard, this user can use several terminals, fixed or mobile, for one and the same subscription to a service provided by the operator. In 3GPP terminology, a terminal is called UE (User Equipment).
It is assumed that this user has an application session in progress in the telecommunications network. By way of example, he is in communication with an opposite party on one of his terminals UE. Currently, the state of the art in 3GPP allows this user to transfer one or more streams of this communication (when the latter comprises several streams, an audio stream and a video stream for example) over to another UE terminal. Thus, a user who has begun a call on his mobile terminal and who arrives at his office can transfer the voice stream over to his fixed terminal, in a transparent manner, that is to say without interruption for his opposite party.
However, a constraint of the technique currently specified in 3GPP within the framework of application session transfer is that, for a given multimedia session, a single terminal, the so-called “Controller UE” (controller terminal), has control of the service. Stated otherwise, only this controller terminal can initiate the transfer of a media stream to another terminal.
According to the document TR 23.838, when a UE participates in the establishment of a communication, it is the controller of this communication. When this terminal decides, upon a user action, to transfer the communication or one or more streams making up this communication to another terminal, he may decide either to transfer control or to retain it. The terminal may also transfer control of the communication to another terminal, the so-called target terminal, without transferring any stream.
The user cannot request a transfer by interacting with a terminal other than the controller terminal. Thus, in the previous example, the transfer may be requested by the user by interacting with his mobile telephone (which is then controller), but not by pressing a key of the fixed telephone.
However, situations exist where it would be preferable for the user to be able to control the session transfer from the target terminal. The case is considered, for example, of a user who has received a link to a video clip on his mobile terminal. He is in the process of viewing this clip when he returns home. It is assumed that members of the user's family join him to view it. But before the end of the clip, the user receives an important call on his mobile terminal. He takes the call immediately. However, the other members of his family would like to continue to view the clip. However, it is not possible to do so from a terminal other than the controller mobile terminal controlling the application session in progress.